Passive physiological monitoring (P2M) system

ABSTRACT

Passive physiological monitoring apparatus and method has a sensor for sensing physiological phenomenon. A converter converts sensed data into electrical signals and a computer receives and computes the signals and outputs computed data for real-time interactive display. The sensor is a piezoelectric film of polyvinylidene fluoride. A band-pass filter filters out noise and isolates the signals to reflect data from the body. A pre-amplifier amplifies signals. Signals detected include mechanical, thermal and acoustic signatures reflecting cardiac output, cardiac function, internal bleeding, respiratory, pulse, apnea, and temperature. A pad may incorporate the PVDF film and may be fluid-filled. The film converts mechanical energy into analog voltage signals. Analog signals are fed through the band-pass filter and the amplifier. A converter converts the analog signals to digital signals. A Fourier transform routine is used to transform into the frequency domain. A microcomputer is used for recording, analyzing and displaying data for on-line assessment and for providing realtime response. A radio-frequency filter may be connected to a cable and the film for transferring signals from the film through the cable. The sensor may be an array provided in a MEDEVAC litter or other device for measuring acoustic and hydraulic signals from the body of a patient for field monitoring, hospital monitoring, transport monitoring, home, remote monitoring.

BACKGROUND OF THE INVENTION

Minimization of the time between injury occurrence and transport to theappropriate level of medical care is necessary to ensure that woundedand sick soldiers obtain the prompt medical attention essential fortheir survival. During that time, aeromedical care in a MEDEVAChelicopter environment is used to identify and transport casualties.

Military units conduct aeromedical evacuations daily during times of warand peace, exposing the patient and flight/medical crew to noise orenvironmental stress and difficult monitoring conditions. As in thecivilian community, military nurses depend on reliable and efficientmonitoring devices to provide accurate patient care in variousenvironments, some of which are hostile and obtrusive to the use ofconventional monitoring instrumentation. While aeromedical evacuation isa life-saving process for many, it is nearly impossible for medicalpersonnel to monitor vital signs in a high noise environment.

Vital signs monitoring is normally a simple and routine procedureinvolving collection of pulse, respiration and blood pressure data. In arelatively quiet environment, these parameters are easily detected.However, acquisition of physiological signals of interest in ahelicopter environment is a challenging problem for several reasons.Limitations on vital signs collection include high noise, vibration,auditory distractions, ineffective monitoring equipment, cramped workingconditions, bulky gear during air evacuation, and electromagneticinterference with aircraft systems caused by some medical equipment. Theadditional complexity of leads and electrodes compounds the noise andenvironmental problems. The physiological parameters of vital signs fallwithin the helicopter-generated frequencies. Helicopter frequencies havea much greater power in those frequencies as well. Vibrational andacoustic artifacts are also major problems. The signal to noise problemmust therefore be solved by other means in addition to low and high bandpass filtering approaches. Due to the limiting work conditions, medicalpersonnel cannot use a stethoscope to accurately monitor heart activityor blood pressure.

The military medical system needs a portable, non-invasive devicecapable of monitoring a soldier's vital signs in the field environmentunder less than ideal circumstances. This system needs to be useful tomilitary medical personnel across the spectrum of care delivery, such asin-mass casualty situations, aeromedical evacuations, ground ambulancetransports, hospital wards, and intensive care units. A recent studyfound that thirty-two percent of aircraft medical devices flown onboarda rotor-wing MEDEVAC aircraft failed at least one environmental test.

Quartz crystals are minerals that create an electric field known aspiezoelectricity when pressure is applied. Materials scientists havefound other materials with piezoelectric properties. The versatility andpotential uses for piezoelectric materials have been known butcost-prohibitive for some time.

However, recent decreases in the cost of manufacturing now permitgreater application by engineers and researchers. The advantageousqualities of piezoelectric materials have been applied to medicine,security, acoustics, defense, geology and other fields. Development ofapplications with piezoelectric materials is in its infancy.

The medical practice and research application of piezoelectric-basedinstrumentation is gaining momentum. Piezoelectric methods have beensuccessfully used in plethysmography, blood pressure monitoring bypiezoelectric contact microphone, heart rate monitoring in avian embryosand hatchlings and piezoelectric probes. Piezoelectric materials areused as detectors of sensitive motion to measure human tremor, smallbody movements of animals in response to pharmacological manipulation,and respiratory motion for nuclear magnetic resonance (NMR) animalexperiments. In combination with ultrasound, piezoelectric methods havebeen used to assess coronary hemodynamics, elastic tensor,intra-arterial imaging, and receptor field dimensions. In addition,piezoelectric transducers have been attached to the chest wall and usedwith automated auscultation devices and microcomputers for lung soundanalysis. Piezoelectric film has been applied and studied to determinejoint contact stress, and piezoelectric disks have been used forrecording muscle sounds and qualitative monitoring of the neuromuscularblock.

Stochastic wave theory, as commonly used in ocean engineering to analyzepseudo-periodic phenomena, indicates spectral peaks from respiration andheart rate. Human heartbeats, respiration, and blood pressure arerepetitive in nature, reflecting complex mechano-acoustical events.However, various problems with piezoelectric instrumentation developmentprevent its full realization. Measurement of human tremor only workswell when the environment is absolutely silent. In fact, extraneousnoise such as equipment, fans, people talking, and the patient's ownvoice routinely exists in most hospital rooms. That noise masks anddistorts the signal of interest, thus limiting the practicality ofpiezoelectric instrumentation. Animal noises make data collectiondifficult in laboratory animal studies. In non-laboratory environments,medical uses of piezoelectric instrumentation for humans remains aproblem because of the inherent signal-noise problem.

A primary mission of military nurses is to ensure that wounded and sicksoldiers obtain prompt medical attention and/or evacuation to definitivemedical care. The actions performed during the time period between abattlefield injury and the transfer of casualties to appropriate medicaltreatment is critical for the welfare of the soldier, and can be thedifference between life and death. It is during this critical timeperiod where diagnosis and treatment begins and also when evacuation—forexample via MEDEVAC helicopter—occurs.

Unfortunately, the extremely high noise and vibration inherent in thehelicopter environment prevents nursing and medical personnel fromaccurately measuring vital signs. Not only are electronic medicalmonitors rendered ineffective with the high vibrations; traditionalmethods of measuring pulse and blood pressure using a stethoscope becomeunreliable in the high noise. Cramped working conditions and bulky gearduring air evacuation exacerbate these problems.

Most conventional methods use devices that employ electrodes, leads,wires, and cuffs to measure one or more vital signs, for example, bloodpressure machine, ECG monitor, pulse oximeter. Existing monitors requiresome sort of attachment and thus are not passive. In addition,conventional equipment is highly sensitive to noise, such as ahelicopter or airplane engines and rotors.

Clearly, what is needed for this common situation is a monitor that canconsistently and accurately measure vital signs during a medicalevacuation where there is high noise and vibration. The monitor beingrelatively autonomous intervention by a nurse or technician is notrequired. With the added capability of telemetry for remote monitoringand communication, information may be forwarded in real-time viawireless communication to the destination where medical personnel andother caregivers are located.

Needs exist to develop better methods and apparatus for physiologicalmonitoring.

SUMMARY OF THE INVENTION

The present invention is known as Passive Physiological Monitoring, P²M,or simply P2M. Data records with vast information, such as bloodpressure, are measured, recorded, and may later be delineated todetermine the physical condition of the subject being monitored.

Recent developments in materials science and data processing havecreated the potential for a new monitoring device using piezoelectricfilm, an electrically active fluoropolymer. Although the medicalapplications of piezoelectric film are still at the infant stage, thetesting of medical instruments is promising.

The cardiovascular system is modeled as a system of pipes, pumps, andother appendices, with the engineering phenomenon known as “waterhammer” as the basis for a working model for data analysis in thecalculation of blood pressure.

“Water hammer” is a compression wave transmitted through the householdplumbing network of pipes and valves when household water is abruptlyshut off. The result is a noticeable sound and the deterioration of theplumbing system. Water hammer is caused by the increase in pipe pressurecaused by sudden velocity change, typically after water is shut offduring a valve closing. The compression wave is described as follows:$\begin{matrix}{c = {\frac{1}{\rho}*\frac{\mathbb{d}P}{\mathbb{d}V}}} & (1)\end{matrix}$

where

c=speed of the compression wave (ft/sec);

dV=change in velocity (V_(initial)−V_(final));

ρ=density of the fluid; and

dP=change in pressure.

Skalak (1966) applied the linearized theory of viscous flow to develop abasis for understanding the main waveform features in arteries andveins. The vascular system is equivalent to a network of non-uniformtransmission lines.

Womersly (1957) had applied those principles to a single uniform tuberepresenting an arterial segment and compared the results to theexperimental data taken in a dog, prior to Skalak's theory. Goodagreement was reported between the measured flow and the flow computedfrom the measured pressure gradient.

Anliker (1968) showed that the dispersion phenomena associated withwaves propagating in blood vessels are potential measures of thedistubility of the vessels and other cardiac parameters. Anliker assumedthat vessels behave like thin-walled cylindrical shells filled withinviscid compressible fluid. More complete models have provided goodagreement.

Karr (1982) studied pressure wave velocity on human subjects anddeveloped a method to determine the pulse propagation speed. Theinvention recognizes that such information may be used to determineplaque buildup, cholesterol concentration on the arterial wall, andarterial wall thickness.

Equation (1) allows for determination of pressure change (dP) from theheart pulsing based on the dispersion relationship between pulse wavevelocity (c) and flow velocity (v). Karr's method measures flow velocityto determine dP, which is related to systolic pressure (pS) anddiastolic pressure (pD).

The new invention measures the pressure energy from heartbeat andrespiration collectively. The heart contribution to the energy spectrumis determined by removing the respiration contribution to the energyspectrum. Respiration energy is filtered out by comparing the energyspectrum calculations of velocity with velocity measures usingelectromagnetic and doppler methods. Since the sympathetic tone mayinfluence blood pressure measurement accuracy, the new monitor can beconfigured for one of its piezoelectric sensors to serve as a dedicateddoppler sensor that uses ultrasonics to adjust interpretations of dataas a function of the sympathetic tone of the patient. The selectiveomission of P2M signals and the selective comparison of P2M sensor datawith data from other parts of the body, as well as comparisons betweentwo or more simultaneously triggered sensors, isolates energycontributions from the heart. P2M energy spectra determined from thefoot differs from spectra derived from the chest area, which provides ameans for isolating heart energy as the foot spectra is largely void ofenergy from respiration.

Once velocity (v) is known, the relation between systolic and diastolicblood pressure (2) and the Bernoulli equation (3) is used to measureblood pressure. The Bernoulli equation is a fundamental relationship influid mechanics that is derived from Newtonian mechanics and theprinciple of conservation of energy. A more compressive version of thesame equation can be developed to reflect more complicated non-steadyflows. $\begin{matrix}{p = {{pD} + {\frac{1}{3}*\left( {{pS} + {pD}} \right)}}} & (2)\end{matrix}$

where

pS=systolic pressure;

pD=diastolic pressure; and

p=average pressure.p=ρgh+½*ρ*V ²   (3)

where

ρ=fluid density,

g=gravitational constant, and

h=height, head energy term.

From these equations we can develop expressions for pD and pS, both as afunction of the pulse wave velocity (c), flow velocity (v) and pulsewave pressure (dP):pD=½*ρ*v ² −ρ*C*dV   (4)pS=pD+ρ*C*dv   (5)

P2M is well-suited to assist medical personnel in several areasincluding, but not limited to, the following situations:

(1) Medical monitoring of vital signs of severely injured persons inhigh noise and vibration environments such as rescue helicopter wherecurrent monitoring techniques are cumbersome or impossible;

(2) Monitoring casualties resulting from major disasters such asaircraft accidents, earthquakes and floods;

(3) Physiological monitoring of large numbers of patients through a“smart stretcher” easily deployed for field use by medical personnel;

(4) Continuous military hospital bed monitoring without disturbingpatients; and

(5) Patient monitoring when treatment is delayed due to temporaryoverload of medical facilities.

The development of the P2M or a passive sensor array (multi-sensorsystem) is a significant innovation in passive monitoring. Through theuse of a grid of passive sensors, noise can be reduced throughcorrelating signals from different pads to discern noise from biologicalsignals. This is very important in high-noise environments.Additionally, the significance of a passive multi-sensor system is thatit affords the opportunity to more comprehensively monitor a patient. Asa tool, the grid of passive sensors provides an innovative way tomonitor patients in adverse ambient conditions. The system provides atool whereby parameters other than blood pressure, heart rate, andrespiration can be measured. These parameters include, but are notlimited to, patient movement and sleep habits, pulse strength overvarious portions of the body, relative blood flow volumes, and cardiacoutput, among others.

The main components of the Passive Physiological (P²M) system are thepassive sensor, hardware for amplification, filtering, data-acquisition,and signal-analysis software. In a preferred embodiment, the singlepassive sensor has dimensions 8″×10″ and is preferably encased in aprotective covering. Leads from the sensor attach to the electronics(amplifier, filter, data-acquisition card, desktop computer) where theraw analog voltage signal is filtered and amplified and converted todigital form. Digital filtering and software manipulation of the data inthe form of frequency analyses are then performed. Finally, signalprocessing techniques are then used to extract physiological informationfrom the digital signal.

The sensor pad is preferably placed directly beneath the back of apatient lying supine on a MEDEVAC litter. The mechanical/acousticsignals created by cardio-pulmonary function are transmitted through thebody onto the passive sensor, which converts the signal into an analogvoltage. An illustration of the existing P2M setup is shown in FIG. 6.Among the major hardware used for the laboratory setup are: desktopcomputer, a multi-function programmable charge amplifier and roll-aroundrack to encase all of the hardware. To maintain versatility for initialresearch and development, most of the equipment were chosen forfunctionality at the expense of space efficiency.

It is an object of the present invention to provide the military medicalcommunity with an inexpensive, non-restrictive, portable, light-weight,accurate, and reliable device that can be used in field or fixedfacilities to provide an accurate measurement of heart rate, respirationand blood pressure in high noise and vibration environments and thusimprove medical care in mass casualty situations, aeromedicalevacuations and hospital settings.

It is an object of the present invention to adjust the signal noise toenable the use of piezoelectric instruments in aeromedical transport ofpatients, hospital bed monitoring, and other applications in themilitary and civilian medical environment.

It is an object of the present invention to develop a prototypephysiological monitor using piezoelectric film in various fieldenvironments. The variables of accuracy, precision, usercharacteristics, and patient comfort determine the value of a fieldinstrument for collection data on vital signs.

It is an object of the present invention to provide a non-invasive meansfor monitoring vital functions without the use of electrical leads orwiring on the patient. The use of the human body's acoustic andelectromagnetic signals to determine heart rate, respirations, and bloodpressure.

These and further and other objects and features of the invention areapparent in the disclosure, which includes the above and ongoing writtenspecification, with the claims and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of the P2M system components.

FIG. 2 is a perspective view of the P2M system.

FIG. 3 is a graphical comparison of the P2M bench test results and thehuman evaluator measurements.

FIG. 4 is a front view of the front panel display and user interface ofthe P2M system in Acquire Mode.

FIG. 5 is a front view of the front panel display of the P2M system inMonitor Mode.

FIG. 6 is a schematic view of a preferred embodiment of the P2M sensor.

FIG. 7 shows one of the graphical user interfaces (GUI) of the P2Msystem.

FIG. 8 shows the graphical user interface of the P2M system showingtime-series and frequency-domain representations of physiological data.

FIG. 9 shows measurement of Pulse-Wave Travel Time (PWTT) FIG. 10 showsa system test and evaluation results in a graph.

FIG. 11 high noise and vibration testing of the P2M at Wheeler Army AirField.

FIG. 12 shows the measurement through a body armor.

FIG. 13 shows testing through body armor and MOPP gear combined.

FIG. 14 shows a schematic view of the Passive Physiological Monitoring(P2M) System Using a passive sensor array and microelectronicsincorporated into a MEDEVAC litter.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred P2M system is a monitoring device with two majorsubsystems, one to measure signals and the other to process data intomeaningful information.

FIG. 1 shows a schematic of the system, and FIG. 2 shows a perspectiveview of the system. First, the piezoelectric film, an electricallyactive fluoropolymer converts mechanical energy such as movement causedby a heartbeat into voltage measurements capable of supporting timeseries analysis techniques. Second, the voltage is recorded by andanalyzed using a microcomputer controlled system, the purpose of whichis to discriminate the signal from background noise and display it on ascreen or printout. Techniques such as preamplifying and preconditioningthrough the use of high and low-band pass filters reduces noise.

The piezoelectric material 1 used is the polymer polyvinylidene fluoride(PVDF), which can be shaped into cables, thin film, or thick tiles. PVDFpiezoelectric film is environmentally rugged, lightweight, flexible,inherently reliable, sturdy, easily repairable and transportable withexcessive assembly or disassembly. Since the material is inert, it maybe used inside the human body. Ultraviolet radiation passes harmlesslythrough the PVDF film, which may be produced in varying thicknesses. Inaddition, the piezoelectric film is waterproof, operates between 0 and145 degrees Centigrade, and does not tear under stress. PVDF may converta temperature reading into an electric output. The PVDF film isincorporated into a fluid-filled vinyl pad, approximately 10 cm by 10 cmin surface area. This is placed on/under/above various locations of thepatient.

P2M detects cardiac and respiratory motion, and monitors pulse,respiration and apnea episodes 3. Cardiac and respiratory movements aresimultaneously recorded by selective filtering of original signal. Thepiezoelectric element 1 is a pressure—sensing detector acting as ahighly sensitive strain gage providing high dynamic range and linearity.Analog signals are fed through a band-pass filter into an amplifier(×200-×5000) 5 and are visually displayed. Analog acoustic signals areconverted to digital values using a multi-channel converter 7 at asampling rate of up to 5 kHz. Data is transformed to the frequencydomain using Fast Fourier Transform (FFT). The system uses amicrocomputer 9 for recording, analysis and presentation of data, whichallows for on-line assessment of data and realtime decisions.

In its simplest mode of operation PVDF piezoelectric film 1 acts as apiezoelectric strain gage. The voltage output is up to four orders ofmagnitude higher than that produced by a nonamplified signal fromcircuitry used with resistive wire. Linearity and frequency response areexcellent. Although similarities to a strain gage exist, current neednot be applied since the device is electrically self-generating. Unlikethe strain gage, the present invention does not produce an electriccharge ad infinitum with sustained stress. The slowest frequency thepolymer film detects is a thousand seconds for an electrical event tooccur, and the highest is one gigahertz (microwave). The piezoelectricfilm is passive and biologically non-hazardous, as opposed totraditional strain gages that require an applied current.

PVDF sheets are commercial off-the-shelf (COTS) products, the type andspecifications of which were chosen based on optimum sensitivity rangeand resilience. Each sheet contains seven-foot attached shieldedtwisted-pair (for noise rejection) leads 11 to transmit the chargeproduced by the sheets.

The piezoelectric sheets 1 are placed under a patient's chest and footor at similarly remote areas of the body, or may be put on like awrapped cuff. The change in pressure exerted by the patient'srespiration and heartbeat causes the piezoelectric film to generatevoltages, which is carried via nonmagnetic miniature coaxial cable 11through a radio frequency filter 13. The signal is then directed to ahigh input-impedance amplifier 5 and computer system 7 for dataprocessing. A conventional oscilloscope and a chart recorder displaysthe output. Respiration and heart rate 15 are then calculated by theenergy spectrum from the time series data.

Several techniques reduce noise and vibration interferences. Activecancellation uses two piezoelectric sensors, one of which is not incontact with the body. The sensor not attached to the body is exposed toenvironmentally acoustic and vibrational signals, while the sensorattached to the body is exposed to environmental as well as bodysignals. Subtraction of one output from the other output yields the bodysignal of interest.

Another preferred technique to reduce noise involves band-passfiltering/band-stop filtering. By identifying the extraneous electronicor acoustic noise and its particular frequencies, band-pass or band-stopfiltering eliminates extraneous signals from the overall signal.

Additionally, signal processing techniques that use a prior knowledge ofthe expected signals extract the desired information from thepiezoelectric signal. Spectral techniques help to identify thefrequencies and amplitudes of the events of interest and discern themfrom extraneous noise.

Cardiac action analysis uses a bandpass frequency limit of 0.1-4.0 Hz,and respiration analysis uses a frequency limit from 0.01-3.0 Hz. Thefiltered cardiac and respiration signals are fed to a recording system.Body movements are analyzed by bandpass filtering the original signalwith frequency limits from 0.1-20 Hz.

Once the signal produced by the film sensor is converted to voltages,amplified and filtered, it is processed through the P2M instrumentation.The hardware equipment includes, but is not limited to, a 586 processorcomputer 9 with enhanced RAM and disk capacity to handle large amountsof data. A board with a range that includes acoustic frequenciesfacilitates data acquisition, signal conditioning and signal processing.

For system operation, a master program 17 combines the three separatesoftware modules of data acquisition/control, signalprocessing/analysis, and data display/user interface. The LabVIEW™ “G”graphical programming language was used for all three subroutineprograms. The analog voltage signal is digitized and analyzed in timeand frequency domains. Routines developed for signal conditioning andanalysis include digital filtering, spectral analysis, auto correlation,and noise—rejection programs. The data is displayed real-time in eitherMonitor or Acquisition mode. Monitor mode displays the current data anddiscards old readings as new updates are processed, while Acquisitionmode saves data for future analysis. The voluminous data must not exceedthe disk-storage capacity of the computer in Acquisition mode.

For protection and ease of transport, the entire P2M system 19 isencased in a metal technical enclosure 21 with casters (not shown) andlocking glass door (not shown), as shown in FIG. 2. The equipment alsoincludes a MEDEVAC stretcher 23 on which the sensor is mounted. Thisdevice may be incorporated into a litter to eliminate the need forpatient attachment or miniaturized as a portable field device in a pursewith a wireless communication setup.

Significant field and analysis testing was conducted to confirm theworkability and accuracy of the P2M system. The piezoelectric filmmeasures mechanical, thermal and acoustic signals. That high sensitivityis necessary to measure vital signals non-intrusively. For pulse rate,the physical beating of the heart is transmitted through the body intothe piezo-film sensor pad as mechanical impulses. The respiration ismeasured by the mechanical impulse transmitted to the sensor based onchest movements. The sensitive piezo-film sensor pad measures allextraneous movement and speech, resulting in a voltage signal outputthat is superimposed upon the physiological signals. As a result,movement or speech by the subject may cause a reading error.

The P2M sensor measures all physical impulses in the measuringenvironment, including the patient's physiological signals, nearby humannoise and activity signals, noise and vibration from the machinery, andelectromagnetic (EM) noise emitted from the lights and instrumentation.While the output signal includes all of these signals, many are too weakto affect the measurement while others such as EM noise corrupt thereading. Running the signal through filters and other signal—processingalgorithms removes the noise. The conditioned signal is then analyzedthrough routines, including a fast Fourier transform (FFT) whichidentifies the primary signal frequencies. For a still, speechlesspatient, the primary frequency is usually respiration, and the secondhighest frequency is heart rate. Patient positioning and frequencyharmonics may complicate the distinction, requiring additional logic toseparate and identify the heart and respiration frequency peaks. Thelogic algorithms must be robust enough to define the respiration andheart peaks for a variety of conditions.

To increase resolution, a large number of high sampling rate data pointswere selected and re-sampled at a lower rate to simplify computation foraccurate analysis. The minimum sampling interval was thirty seconds.

FIG. 3 shows the results for the twenty respiration/pulse-ratemeasurements performed with the P2M system. Human evaluator measurementswere performed simultaneously as a control. P2M accurately measuredpulse 25 and respiration 27 under ideal conditions, but patient movementor speech interfered with accurate measurement. Heart rate measurementquality was not reduced by the absence of respiration, and P2M matchedthe control measurement results 29, 31 with an error of less than beatper minute.

FIG. 4 shows the P2M front panel in Acquisition mode. The upper graph 33displays a thirty-second window of time-series measurements of allphysiological signals. Heartbeat spikes are shown in the upper (timeseries) graph 33, along with a lower-frequency sinusoidal function whichcorresponds to the respiration signal. The lower graph 35 shows the samedata in the frequency domain. The first and largest spike 37 correspondsto approximately 16.4 respirations per minute. The control group 31measured 17±2 respirations per minute. The large amplitude of the spikeindicates that respiration is the largest impulse measured by the sensorpad. The second-largest spike 39 is sixty times per minute, which wasidentical to the actual heart rate measured by a fingertip-clipheart-rate monitor. The power as measured by the amplitude is less thanone-third of that found in the respiration frequency, but the ratiovaries based on the physiology and sensor pad positioning of thepatient. The smaller spikes 41 in the lower graph represent respirationand heart-rate harmonics, a result of the harmonics not being a perfectsinusoidal function. Since the heart rate might fall at exactly the samefrequency as a respiration harmonic, it is necessary for logicalgorithms to check for harmonics. The heart rate and respirationharmonics may be differentiated by comparing signals taken fromdifferent parts of the body.

The buttons and menus 43 on the front panel of the interface programenables the control of data acquisition and analysis routines. Thethirty-second data records may be saved to file for archiving oradditional evaluation.

FIG. 5 shows the P2M system in Monitor mode. The top graph 45 shows thetime-series data, with the characteristic higher-frequency heartbeatspikes 47 superimposed over a lower—frequency respiration wave 49. Themiddle graph 51 shows heart rate 53 and respiration 55 as updated everyfive seconds. As a new five-second data string is acquired, the oldestfive seconds of data is discarded, and the heart rate and respirationare re-calculated by analyzing the thirty-second data string with thenew data. The upper curve 53 is colored red to signify heart rate, whilethe lower curve 55 is colored blue to signify respiration. Heart rateappears steady in the mid-50s range, with respiration in the mid-teens.Both compare favorably (±2) with human control measurements. The anomaly57 after 25 updates is attributable to patient movement or an extraneousand errant noise/vibration event. The bottom graph 59 shows an FFT ofthe time-series signal.

Regular voltage signals of heart beat provide strength signals asvoltage levels that are related to blood pressure. Times between signalsat varied parts of the body or patterns of secondary signals provideinformation on circulation or blockage or interference with blood flow.

In another preferred embodiment, FIG. 6 shows a schematic view of theP2M system with a single passive sensor 61 positioned on a patient 63.FIG. 7 shows one of the graphical user interfaces (GUI) of the P2Msystem. The upper chart 65 shows a 30-second window of digital voltagedata, where the low-frequency oscillations are caused by respiration andthe higher-frequency spikes are the result of heartbeat measurements ofthe patient on the litter. The time-series signal is converted tofrequency data via a Fourier transform and displayed as a powerspectrum, shown in the middle chart 67. From this data, pulse andrespiration can be extracted by examining the power associated with thedominant frequencies 69.

In a preferred method of blood pressure measurement passive measurementof blood pressure (systolic and diastolic) may be conducted using pulsewave analyses. Measurement and characterization of the pulse-wavevelocity (PWV), or alternately, the pulse-wave travel time (PWTT),inherently requires more than one measurement location. Thus, pluralsensors are required for measurements in different locations. Thesensors may measure pulse-wave characteristics, for example, along thebrachial artery, along with other measurements described herein.

FIG. 8 shows measurement results of the pulse at two locations along thearm. The temporal separation between the two corresponding peaks 71, 73gives the Pulse-Wave Travel Time (PWTT). This value can be used tocorrelate systolic and diastolic blood pressure. As such, thecalibration must be performed simultaneously for several measurements ofPWTT and blood pressure to construct a calibration curve. Barschdorff &Erig showed that the relationship between blood pressures (systolic anddiastolic) are approximately linear with PWV and PWTT.

Testing and evaluation of the P2M system was performed at TAMC inFebruary, 1998. Simultaneous measurements of pulse and respiration wereperformed with the P2M, an electronic monitor, and by human evaluation.FIG. 9 shows a photograph of the testing performed at TAMC. A total of11 volunteers were monitored following the project's testing protocol.

FIG. 10 displays the results of the testing. The P2M was over 95%accurate as compared to conventional methods, and the several instanceswhere the P2M was not in agreement with conventional methods proved tobe very valuable in subsequent modifications and improvements to thesystem software. In addition, 12 volunteer nurses performedphysiological monitoring of pulse and respiration using the P2M,electronic monitor, and human evaluation. Following the monitoring, thenurses completed a survey comparing and ranking the usage of the threemethods.

Testing of the P2M system for pulse and respiration in a high noise andvibration environment was performed at Wheeler Army Air Field, on Mar.5, 1999. Tests were-performed during static display of a MEDEVAChelicopter. The main purpose of the test was to characterize the highnoise/vibration environment using the P2M, microphones andaccelerometers. Results showed that through filtering and signalanalyses, the P2M was able to discern physiological signals from thehigh amplitude and frequency noise caused by the helicopter to outputaccurately pulse and respiration. No conventional methods were performedat this test due to the high-noise environment, which would render thosemethods useless.

FIG. 11 shows the high noise and vibration testing of P2M at WheelerArmy Air Field, on Mar. 5, 1999.

Next, in response to inquiries made by the flight medics during the Mar.5, 1999 testing at Wheeler, the ability of P2M system to accuratelymonitor pulse and respiration through layers of clothing and gear wastested. Fragmentation protective body armor, Military OrientedProtective Posture (MOPP) gear, and a combination of the two were testedusing the P2M system. Results showed that the P2M performed with higherfidelity with the additional layers between the subject and the sensor,which is largely due to the increased contact area and efficienttransmission of mechanical and acoustic signals through the solidlayers.

The single-sensor P²M configuration that has been demonstrated toaccurately measure pulse and respiration is very sensitive to thepatient position relative to the main sensor pad. The quality andmagnitude of the physiological signals received by the system depends onthis positioning. The preferred optimum placement is to situate thesensor directly beneath the center of the patient's chest. If the sensoris moved from this placement, or if the patient position changes, theintegrity of the incoming signal also changes. Thus, a preferredconfiguration uses multiple sensors in a pattern that covers the entireregion of the litter on which the patient would lie so that regardlessof patient movement and position, there will always be one or moreactive sensors in optimum measurement placements.

In a preferred embodiment, the invention is a passive system using anarray of distributed sensors (or “multi-sensor”) capable of accuratelyand robustly monitoring certain physiological signals of the human body.These signals, in turn, may be processed for determination of vitalsigns that are currently used by nurses and other caregivers, forexample, heart rate, respiration, and systolic/diastolic blood pressure.

Passive monitoring of such parameters as cardiac output, cardiacfunction, and internal bleeding are within the scope of this invention.The invention uniquely provides a device that is passive (completelynon-invasive), unobtrusive, and autonomous; i.e., the apparatus in noway interferes either with the patient's mobility or with othermonitoring equipment, and is capable of functioning with a minimum oftechnical expertise. In addition, the equipment functions reliably inhigh-noise environments and other situations that render alternative andexisting methods ineffective. These environments include, but are notlimited to, medical evacuation (MEDEVAC) by helicopter or ambulance, andoperation through Military Oriented Protective Posture (MOPP) gear andbody armor.

With the development of a reliable multi-sensor monitoring system forsuch rugged and noisy operation, the application to the hospital ICUenvironment, where noise is substantially lower, is considerably morestraightforward. Completely non-invasive, passive, pulse, respiration,blood pressure (and detection of cardiac output, internal bleeding,shock, etc.) measurements using a sensor system that is undetectable tothe patient have considerable intrinsic value even in noise-freesurroundings. The passive and autonomous operation of such a system issuitable for telemetry and real-time remote monitoring, and the finalfeature of the invention is a telemetry design feature for distance andremote monitoring.

FIG. 14 shows a schematic of the P2M using a passive sensor array andmicroelectronics incorporated into a MEDEVAC litter. A schematic of theinventive technology, incorporated into a MEDEVAC litter, is shown inFIG. 14 below. The litter 75 is covered in an array 77 of 32 sensors,each of which can measure acoustic and hydraulic inputs from the patient63. Each of these signals contains a measure of physiologicallygenerated signal and environmental noise. The environmental noise oneach pad will be similar, whereas the physiologically generated signalsmay be position dependent. This information is used to separate thesignal from the noise using proven techniques. Position dependentphysiological signals are used to determine patient position, heartrate, respiration, blood pressure, pulse strength distribution, andpotentially some measure of cardiac output.

The invention may be incorporated into a wide range of applicationsapart from the MEDEVAC litter. The passive sensor array may beconfigured without much change to operate on a hospital bed or anordinary mattress used at home. Of particular note is the area ofpremature infant care. In this case, the attachment of sensor leads tothe infant may often be difficult, causing irritation of sensitive skinand entanglement in leads. The sensor may be incorporated into equipmentfor use in both civilian and military sectors. The sensor may beincorporated into field equipment, clothes and uniforms. This includes,but is not limited to, cervical collars, body armor, biological and/orchemical hazard protection suits, extraction devices, clothes, cushionson seats and seatbacks. Exercise equipment, such as stationary bicycles,treadmills or steppers may benefit by incorporating sensors into thesupports.

Physiological indicators such as heart rate may be detected throughhandholds as an aid to regulating the exercise regime. Other usefulapplications might include the use of a passive sensor system in a chairor couch used for psychological examinations. Scrutiny of the subject'sphysiological signs may give indications of emotional disturbance causedby trigger words or events during counseling. The size of each sensor,number of sensors in the array, and configuration of the sensor arraymay be tailored, without much experimentation, to particular needs andsituations. For a mattress, for example, 32 or more sensors in arectangular array may be required.

The preferred passive sensor may use piezo-electric films and ceramics,hydrophones, microphones or pressure transducers. Amplification hardwaremay include signal amplification circuitry and hardware, e.g., chargeamplifier. Data acquisition hardware and signal processing hardware(circuitry) and software are used in the system. For the interfacebetween sensor and patient either solid, fluidized (air) or fluid layermay be used, as for example, gel, water, foam, rubber, plastic, etc. Theinterface facilitates transmittal of physiological signals.

The invention has great medical value for field monitoring, hospitalmonitoring, transport monitoring, and home/remote monitoring. Forexample, the invention may have application in every hospital forpassive monitoring of patients. The invention being undetectable to thepatient, which adds comfort to the monitoring process.

While the invention has been described with reference to specificembodiments, modifications and variations of the invention may beconstructed without departing from the scope of the invention.

1. Passive physiological monitoring apparatus comprising at least one sensor for sensing data by placing the at least one sensor on a body, a converter communicating with the at least one sensor for converting sensed data into signals, a computing device communicating with the converter for receiving and computing the voltage signals and for outputting computer data, and instrumentation communicating with the computing device for real-time interaction with the device and for display of the computed data. 2-46. (canceled) 